Battery manufacturing requires disparate processing of the cathode, anode and separator materials. This causes high production costs that remain a barrier to adoption in key electric vehicles and grid storage markets. Conventional lithium ion cell production consists of slurry coating the anode and cathode materials onto the current collectors that may be referred to as foils, typically in separate rooms. They are then calendared, which involves pressing them flat, drying them and re-reeling the foils. The foils are then slit to the size required and re-reeled. During cell assembly, the anode and cathode are subsequently laminated together with the separator material in between and packaged into a can or case during final assembly. This process typically involves 6 or more wind/unwind (reeling) operations, each having their own costs and possible yield losses.
Current methods of multilayer coating typically employ a slot or slide coater. These tools can coat up to 3 layers simultaneously by stacking the dies or distributions plates. However, lower viscosity pastes with lower particulate loading do not have adequate control of layer boundaries. Depending upon the viscosities of the pastes, the dies or print heads used in these methods may also have speed limitations, as discussed in U.S. Pat. No. 7,700,019.
The approach in U.S. Pat. No. 7,700,019 proposes a method of using multi-layer extrusion with slot dies for fabricating vertical layers of electrode material on current collectors with a sheet of polymer electrolyte. This patent discloses slot coating and cannot handle high particulate loading or viscosity of paste that provide better battery structures.
Another approach is disclosed in U.S. Pat. No. 7,799,371 in which a multi-layer metal stack fabricated by individual orifice outlets such that layers of dispensed paste lie on top of each other. In this approach, the materials merge together and form the multi-layer structure outside the printhead. This may cause issues with registration between the layers if the substrate or the print head shifts during deposition.
A co-extrusion print head, as opposed to a slot coater, and a co-extrusion process has been discussed in several US Patents and US Patent Applications. Examples of these types of battery electrodes are discussed in U.S. Pat. Nos. 7,765,949; 7,780,812; 7,922,471; and US Patent Publications 20120156364 and 20120153211. U.S. Pat. No. 7,765,949 discloses a device for extruding and dispensing materials on a substrate, the device has at least two channels for receiving materials and an exit port for extruding the materials onto the substrate. U.S. Pat. No. 7,780,812 discloses another such device having a planarized edge surface. U.S. Pat. No. 7,922,471 discloses another such device for extruding materials that have an equilibrium shape that does not settle after deposition onto the substrate. US Patent Publications 20120156364 and 20120153211 disclose a co-extrusion head that combines streams of two or more materials into an interdigitated structure on a substrate, where there are multiple stripes of the materials. None of these discussions address co-extruding multi-layer structures.